The over all best buffer for discus water I think is peat-moss, it will turn the water a light tea color, but offers lots of good effects and no bad ones that I am aware of. Since acidic waters have low pH ( 6.9 and lower ) buffers are required to "stablize" the pH. A natural buffer in fresh water is KH or calcium and magnesium carbonates. The chemical powders we can buy to buffer pH may be these carbonates and will increase KH "hardness" while keeping the pH from easily shifting up or down. Other powder products we can buy may be "non carbonate" buffers which still hold pH stable, but do not increase KH, but do add other ions to the water. This is usually only a factor when breeding discus.